Re: [CAD_CAM_EDM_DRO] lifetime...

In a message dated 12/8/2002 5:10:51 PM Central Standard Time,
jipeess2000@... writes:

> . . . how this and that will improve the lifetime for a certain component,
> so, does anyone know the estimated lifetime for a g201, and how should it
> be arranged to achive optimized functionality and lifetime.

JS:

I am NOT a graduated EE (though I tried, 40 years ago), but, other than
Mariss and Jon and a couple of others whose names I have not yet memorized,
it seems clear that electrical engineering basics are perhaps as foreign to
us as are the basics of metalworking to most EE's.

Thus, as I THINK I can answer your question adequately in this regard, I will
try to do so. But I also would beg Mariss and Jon, et al, with more brains
to BETTER-respond, as well!

Electrical components have not just the "electrical values" for which they
are made, such as OHMS for resistors and FARADS for capacitors, but "stress
limits" beyond which if they are stressed they will quickly go to the
hereafter for electrical components. For example, RESISTORS have "wattage
ratings". Basically, small ones may withstand only a fraction of a watt, and
large ones, say for old-fashioned unipolar stepper-motor ballast use, might
have 100-watt ratings. If you apply enough voltage across a resistor made to
dissipate 1/4 watt to CAUSE it to dissipate 1 whole watt, it will go up in
smoke rather quickly. Likewise, if you apply 100 volts DC across a capacitor
made for use below 50 volts, it might SEEM to work OK for a moment, but
probably will "pop" (often loudly, and with acrid smell and smoke!) quickly.
But if you applied 50 volts across a capacitor DESIGNED for 50 volts, and
leave that voltage applied for many, many hours, chances are it would "pop"
with a surprise. To preclude such "infant death", we EE-types try to
"derate" components. An example of this would be to use 75 volt or 100 volt
capacitors on a 50-VDC-max. circuit.

Now, I have never studied the schematics of the Gecko drives, but I ASSUME
that the "chopping" they employ to limit average current is stressful to
internal bypass capacitors inside, and this can become particularly nasty to
po' li'l capacitors when the "peaks" caused by such chopped DC must "travel
back" along 18" lines (wires) to the power-supply's filter-capacitors. This
is difficult to explain in words, particularly for this po' ol' dummy, but I
try!

So, if you put that 470 uF capacitor "right ON the DC-input terminals" of the
Gecko-drive, these "nasty transients" are "stopped cold", and cause much,
much less stress to other components "in there". Besides, it will preclude
"broadcasting" of these electrical nasties through the air, where they can
have evil effects upon radios, inadequately-bypassed logic-circuitry nearby
("computer stuff", in other words), and other sensitive electrical things
which are often offended by EMI eminating from other than 50 or 60 Hz.
PURE-sine-waves.

Further, if a circuit, even a beautifully-engineered and assembled thing like
the G2xx circuits, is "rated" to handle "up to 7 amps" and "up to 80 volts",
it will FUNCTION just fine with those voltages and currents raging through
them, when installed, and probably will for many hours of practical use.
But, were I asked to bet on the first to fail, that one, or one driving a
stepper drawing only 2 amps per winding, and using a 30 VDC supply, I'd bet
it'd be the one on 80 volts! Note, however! This is a totally UNscientific
guess! I have actually NO empirical data to support this assumption!

I hope I have not simply further-confused things! I tried NOT to! Duh . .
. Jan Rowland


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